Optical power transfer and communication methods for wireless implantable sensing platforms

Ultrasmall scale implants have recently attracted focus as valuable tools for monitoring both acute and chronic diseases. Semiconductor optical technologies are the key to miniaturizing these devices to the long-sought sub-mm scale, which will enable long-term use of these devices for medical applications. This can also enable the use of multiple implantable devices concurrently to form a true body area network of sensors. We demonstrate optical power transfer techniques and methods to effectively harness this power for implantable devices. Furthermore, we also present methods for optical data transfer from such implants. Simultaneous use of these technologies can result in miniaturized sensing platforms that can allow for large-scale use of such systems in real world applications

NIR light transmission through skin and muscle

Light has been used extensively in the medical field for both therapeutic and diagnostic applications. Tissue optical window or therapeutic window defines the range of wavelengths where the light has the maximum transmittance through tissue. In this range, absorption and scattering effects are relatively lower when compared to the visible or middle infrared wavelengths. Knowledge of the transmittance through tissue can help determine the effective light intensities in medical applications. The objective of this thesis is to determine the NIR light transmission through different thicknesses of animal tissue and its spatial spread due to the scattering effect. Primarily pork skin and muscle tissues are used due to their similar optical properties to human tissue. Tissue thicknesses range from 4 mm to 20 mm. A NIR LED array with the wavelength of 875 nm serves as the light source. A commercial photodiode is used for measurements of the transmitted light intensities. The results demonstrate a transmittance of 18% for 4 mm tissue thickness and 3% for 20 mm and vary exponentially in between. Scattering increases the spatial spread of the light beam and makes it very difficult to focus inside the tissue. In addition to the transmittance measurements, temperature elevation due to the NIR light illumination is investigated. Thermocouple measurements show a temperature increase of 1.2 °C on the surface of the tissue slab at the light intensities tested in this project

Channel modeling and characterization for VLC-based medical body sensor networks: trends and challenges

Optical Wireless Communication (OWC) refers to transmission in unguided propagation media through the use of optical carriers, i.e., visible, Infrared (IR), and Ultraviolet (UV) bands. In this paper, we focus on indoor Visible Light Communication (VLC)-based Medical Body Sensor Networks (MBSNs) which allow the Light Emitting Diodes (LEDs) to communicate between on-body sensors/subdermal implants and on-body central hubs/monitoring devices while also serving as a luminaire. Since the Quality-of-Service (QoS) of the communication systems depends heavily on realistic channel modeling and characterization, this paper aims at presenting an up-to-date survey of works on channel modeling activities for MBSNs. The first part reviews existing IR-based MBSNs channel models based on which VLC channel models are derived. The second part of this review provides details on existing VLC-based MBSNs channel models according to the mobility of the MBSNs on the patient’s body. We also present a realistic channel modeling approach called site-specific ray tracing that considers the skin tissue for the MBSNs channel modeling for realistic hospital scenarios.Scientific Research Projects (BAP) (Grant Number: 20A204)Publisher's Versio

Conception d'un système de biotélémétrie optique transcutanée

Les personnes qui se sont vues amputées d'un membre peuvent retrouver une partie de leur autonomie et de leur qualité de vie grâce à l'utilisation d'une prothèse adaptée à leurs besoins.Les récentes avancées technologiques dans le domaine de la prothétique laissent entrevoir qu'il sera bientôt possible de commander les mouvements d'une prothèse motorisée à partir de l'interprétation des influx nerveux qui auraient été destinés aux muscles du membre maintenant amputé. Pour ce faire, les impulsions nerveuses seront mesurées par un dispositif totalement implantable et celui-ci devra transmettre en temps réel les données recueillies vers la prothèse à l'aide d'un système de biotélémétrie. Si cette transmission de données requiert une bande passante élevée et une grande qualité du lien de communication, cela se traduira par une consommation énergétique plus élevée. Or, les circuits électroniques du dispositif implanté étant alimentés par une pile, cette consommation énergétique devra être minimisée. Les systèmes actuels de biotélémétrie utilisent le couplage inductif ou les ondes radio afin de transmettre les données, mais ces systèmes ne peuvent rencontrer à la fois les contraintes de faible consommation énergétique et de capacité élevée de transmission qu'impose une prothèse à commande neuronale. Afin d'y parvenir, un système de télémétrie optique transcutané qui utilise les propriétés optiques des tissus cutanés est proposé. Il a été conçu dans le but de transmettre des données à un débit de 16 Mb/s et à un taux de bits erronés de 1E-9 en consommant une puissance de 10 mW. Ce mémoire présente l'impact du taux de transmission des données sur la consommation énergétique du transmetteur, de même qu'une mesure de la puissance requise pour assurer une transmission à travers des tissus cutanés d'épaisseurs variées. La sensibilité du système à un désalignement entre l'émetteur et le récepteur a également été étudiée

A Three – tier bio-implantable sensor monitoring and communications platform

One major hindrance to the advent of novel bio-implantable sensor technologies is the need for a reliable power source and data communications platform capable of continuously, remotely, and wirelessly monitoring deeply implantable biomedical devices. This research proposes the feasibility and potential of combining well established, ‘human-friendly' inductive and ultrasonic technologies to produce a proof-of-concept, generic, multi-tier power transfer and data communication platform suitable for low-power, periodically-activated implantable analogue bio-sensors. In the inductive sub-system presented, 5 W of power is transferred across a 10 mm gap between a single pair of 39 mm (primary) and 33 mm (secondary) circular printed spiral coils (PSCs). These are printed using an 8000 dpi resolution photoplotter and fabricated on PCB by wet-etching, to the maximum permissible density. Our ultrasonic sub-system, consisting of a single pair of Pz21 (transmitter) and Pz26 (receiver) piezoelectric PZT ceramic discs driven by low-frequency, radial/planar excitation (-31 mode), without acoustic matching layers, is also reported here for the first time. The discs are characterised by propagation tank test and directly driven by the inductively coupled power to deliver 29 μW to a receiver (implant) employing a low voltage start-up IC positioned 70 mm deep within a homogeneous liquid phantom. No batteries are used. The deep implant is thus intermittently powered every 800 ms to charge a capacitor which enables its microcontroller, operating with a 500 kHz clock, to transmit a single nibble (4 bits) of digitized sensed data over a period of ~18 ms from deep within the phantom, to the outside world. A power transfer efficiency of 83% using our prototype CMOS logic-gate IC driver is reported for the inductively coupled part of the system. Overall prototype system power consumption is 2.3 W with a total power transfer efficiency of 1% achieved across the tiers

Wireless Electrostimulation to Eradicate Bacterial Biofilms

Bacterial biofilms can form on medical implants and cause serious device-associated infections that are incurable by conventional antibiotics because of high-level tolerance to antimicrobials. Common strategies for controlling device-associated infections, such as coating with antimicrobials and modification of surface properties, can reduce or delay biofilm formation, but the inhibitory effect can be overcome by bacteria over time, and eradicating mature biofilms remains challenging. Direct currents (DCs) have been shown to have bactericidal effects and synergy with conventional antibiotics in concurrent treatment has been demonstrated for killing biofilm cells. However, these systems require a direct connection between electrodes and a power source, which requires skin-piercing wiring for current delivery. This is an invasive process that causes discomfort and can lead to secondary infections. In this study, we developed a new method to achieve DC treatment wirelessly towards the non-invasive control of device-associated infections. Pseudomonas aeruginosa PAO1 and Staphylococcus aureus ALC2085 were used as model organisms to investigate the killing efficacy of wirelessly delivered DC. In the proof-of-concept experiments, we demonstrate that antibiotic tolerant biofilm cells can be effectively eradicated by electromagnetically induced DC from a remote power source. For example, the number of viable P. aeruginosa and S. aureus biofilm cells was reduced by approximately 3.4 and 2 logs, respectively, after treatment with 60 µA/cm2 of wirelessly delivered DC using stainless steel electrodes for 6 hours. DC generated with graphite-based TGONTM electrodes was also effective especially against S. aureus. For example, the viability of P. aeruginosa and S. aureus biofilm was reduced by 1.4 and 2.5 logs, respectively, after treatment with the 30 µA/cm2 of wirelessly delivered DC for 3 hours. Synergy in biofilm killing was also observed between lower level DC and antimicrobials (tobramycin and chlorhexidine for P. aeruginosa and S. aureus, respectively). These conditions were found safe to both human lung epithelial cells and mouse fibroblast cells. Additionally, the viability of S. aureus and Streptococcus mutans biofilms on the denture material were also reduced by 5 and 4 logs, respectively, by the concurrent treatment with the 28 µA/cm2 of DC and 50 µg/mL chlorhexidine for 1 hour. To further evaluate the potential of this technology, we engineered a prototype device after comparing different device designs with varying shapes, electrode layouts, and electrode materials. The prototype device based on the selected design demonstrated 1.0 and 2.6 logs of killing of P. aeruginosa and S. aureus biofilms, respectively, with 6 µA/cm2 of wirelessly delivered DC for 6 h using an ex vivo model with porcine skin. Further in vivo test using a rabbit model showed that the prototype device inserted under the dermis tissue killed S. aureus biofilm cells by 65 % in vivo when receiving a magnetic field from outside of the body to generate DC. No tissue damage was found according to the histological analysis. The killing mechanism of DC treatment was investigated in this study by comparing the killing effects of different electrochemical products. The results show that DC treatment using TGON electrodes killed bacterial cells by generating hypochlorite from the anode; while the DC treatment using stainless steel electrodes induced Fenton reaction and generated free radicals that have potent bactericidal effects. In summary, the findings from this study indicate that wirelessly delivered DC has promising anti-biofilm effects on bacterial pathogens, both in vitro and in vivo. To our best knowledge, this is the first study to report the bactericidal activity of wirelessly delivered DC treatment. With the capability to kill bacterial biofilm without using a directly connected power source, this platform technology has potential applications for noninvasive treatment of biofilm infections associated with orthopedic, cochlear and other implanted medical devices

Integrated Microsystems for Wireless Sensing Applications

Personal health monitoring is being considered the future of a sustainable health care system. Biosensing platforms are a very important component of this system. Real-time and accurate sensing is essential for the success of personal health care model. Currently, there are many efforts going on to make these sensors practical and more useful for such measurements. Implantable sensors are considered the most widely applicable and most reliable sensors for such accurate health monitoring applications. However, macroscopic (cm scale) size has proved to be a limiting factor for successful use of these systems for long time and in large numbers. This work is focused to resolve the issues related with miniaturizing these devices to a microscopic (mm scale) size scale which can minimize many practical difficulties associated with their larger counterparts currently. To accomplish this goal of miniaturization while retaining or even improving on the necessary capabilities for such sensing platforms, an integrated approach is presented which focuses on system-level miniaturization using standard fabrication procedures. First, it is shown that a completely integrated and wireless system is the best solution to achieve desired miniaturization without sacrificing the functionality of the system. Hence, design and implementation of the different components comprising the complete system needs to be done according to the requirements of the overall integrated system. This leads to the need of on-chip functional sensors, integrated wireless power supply, integrated wireless communication and integrated control system for realization of such system. In this work, different options for implementation of each of these subsystems are compared and an optimal solution is presented for each subsystem. For such complex systems, it is imperative to use a standard fabrication process which can provide the required functionality for all subsystems at smallest possible size scale. Complementary Metal Oxide Semiconductor (CMOS) process is the most appropriate of the technologies in this regard and has enabled incredible miniaturization of the computing industry. It also provides options for designing different subsystems on the same platform in a monolithic process with very high yield. This choice then leads to actual designs of subsystems in the CMOS technology using different possible methods. Careful comparison of these subsystems provides insights into different design adjustments that are made until the desired functions are achieved at the desired size scale. Integration of all these compatible subsystems in the same platform is shown to provide the smallest possible sensing platform to date. The completely wireless system can measure a host of different important analyte and can transmit the data to an external device which can use it for appropriate purpose. Results on measurements in phosphate buffer solution, blood serum and whole blood along with wireless communication in real biological tissues are provided. Specific examples of glucose and DNA sensors are presented and the use for many other relevant applications is also proposed. Finally, insights into animal model studies and future directions of the research are discussed. </p